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Congruence of Triangles and Inequalities in a Triangle — MATHS STD 9 — Question

Rajasthan BoardEnglish MediumSTD 9MATHSCongruence of Triangles and Inequalities in a Triangle1 Mark
Question
In $\triangle\text{ABC, AB = AC}$ and $\angle\text{B}=50^{\circ}.$ Then, $\angle\text{A = } ?$
  1. 40°
  2. 50°
  3. 80°
  4. 130°
✓

Answer

  1. 80°
Solution:
In $\triangle\text{ABC,}$
$\text{AB = AC}$
$\Rightarrow\angle\text{C}=\angle\text{B}$ (angles opposite to equal sides are equal)
$\Rightarrow\angle\text{C}=50^{\circ}$
Now, $\angle\text{A}+\angle\text{B}+\angle\text{C}=180^{\circ}$
$\Rightarrow\angle\text{A}+50^{\circ}+50^{\circ}=180^{\circ}$
$\Rightarrow\angle\text{A}=80^{\circ}$

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